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This question already has an answer here:

You all know smartphone headsets. Most of them have a microphone integrated and additional pushbuttons for increasing/decreasing the volume or to pause the current track. I am wondering how this is working. The plug has 4 pins. I assume one pin is GND, two are for left and right audio and the fourth is for the microphone. So how are the pushbuttons connected then? There are three pins missing.

Maybe the microphone pin is used as bidrectional pin? If it is so there must be a protocol which declares which button was pressed (like UART). Also I don't know where the power suppy should come from. All the headset gets is an analog audio signal from the master device.

Connector:

Connector

Pushbuttons:

enter image description here

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marked as duplicate by RedGrittyBrick, Leon Heller, PeterJ, Chetan Bhargava, Joe Hass Jan 12 '14 at 12:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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An image is a thousand words so here is an image that visualizes the connection scheme of three buttons

enter image description here

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  • \$\begingroup\$ This really answers it! I would like to keep this question open because your answer is short and helpful. \$\endgroup\$ – arminb Jan 12 '14 at 1:32
  • \$\begingroup\$ @arminb Sure, why not. Maybe somone can provide more details on the internals but on the plug side it's as simple as shorting the mic pins directly or through resistances of different values. \$\endgroup\$ – alexan_e Jan 12 '14 at 1:52

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